An optical fiber has typically a small average diameter of 0.1 to 1 mm and is drawn in the form of a single strand, and therefore, the quality of the optical fiber may be influenced even by a minor change in the electric potential or the tensile strain applied thereto during the producing procedure.
An optical fiber after drawn is continuously subjected to several coating steps with various coating materials such as a primary coating material, a secondary coating material, an ink composition, and a ribbon coating material, for various purposes. Accordingly, studies on the coating of an optical fiber has been mainly made in aspect of an enhancement on the curing speed of the coating composition, and, recently, a photocurable composition has been widely used, rather than a thermally curable composition, due to its high energy-efficiency, short reaction time and simple production equipments.
During the producing procedure, on the other hand, an optical fiber is conveyed at a very high speed, and thus, the surface of the fiber is charged with static electricity by the action of frictional force between the fiber and the conveying apparatus and further the static electricity thus generated accumulates on the surface of the fiber due to the resin component coated on the fiber. That is, the surface of an optical fiber is always in an electrically charged condition all through the producing process.
The static electricity present on the surface of the fiber causes the problems that it generates a repulsive power between the fibers, thus lowering the productivity of the fiber, it makes the fiber to be easily contaminated, and it makes the coated layer to be non-uniform, thus lowering the optical and mechanical properties of the fiber.
To remove the static electricity of an optical fiber, the optical fiber is conventionally passed through an antistatic apparatus installed in the fiber producing system. However, in this method, the static electricity is just temporarily removed, not permanently, and the antistatic apparatus generates a large amount of heat and involves a risk of electric shock.